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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1658) A less expensive way to figure out directory size
Date Mon, 28 Feb 2011 17:26:36 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1658?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13000414#comment-13000414
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Tsz Wo (Nicholas), SZE commented on HDFS-1658:
----------------------------------------------

> ... But still an application needs to call getFileInfo first. After it figures out the
path is a directory, ...

It is unnecessary to call getFileInfo first since whether a path is a directory can be determined
by the file/directory counts returned by {{getContentSummary(..)}}.

We have two solutions:
# Change {{FileSystem.getFileInfo(..)}} to return the number of children in {{FileStatus.length}}.
# Add a new {{FileSystem.getContentSummary(..)}} method with _depth_ as a parameter.

\\
#1 is a semantic change but #2 is not.  I am afraid that there may be user codes relying on
the fact that {{FileStatus.length == 0}} when the path is a directory.


> A less expensive way to figure out directory size
> -------------------------------------------------
>
>                 Key: HDFS-1658
>                 URL: https://issues.apache.org/jira/browse/HDFS-1658
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>
> Currently in order to figure out a directory size, we have to list a directory by calling
RPC getListing and get the number of its children. This is an expensive operation especially
when a directory has many children because it may require multiple RPCs.
> On the other hand when fetching the status of a path (i.e. calling RPC getFileInfo),
the length field of FileStatus is set to be 0 if the path is a directory.
> I am thinking to change this field (FileStatus#length) to be the directory size when
the path is a directory. So we can call getFileInfo to get the directory size. This call is
much less expensive and simpler than getListing.

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